ironman wroteHello Kareem,
Well, according to the NAS, Disk 2 became "Unrecognized", i tried to plug it on Windows, it worked normally....
I even tried to check the disk under Windows (Bad Sectors)...
Concerning the backup NAS, i read about this Photorec that i can copy to the NAS and launch it via Putty. And as you said, it can take days, and i would need a 6TB External drive to recover the files to, AND the worst thing is that it doesnt recover file names nor the folder structure... I think that would be my last resort.
It would recover filename if the filesystem is intact. Unless you have a corrupted file filesystem, you should be good to go.
I had two 10TB drives so it took me 1 week.
What I would do is connect the 3 drives to windows and install Linux ext4 reader it's a freeware (
https://www.diskinternals.com/linux-reader/)
In my case windows was able to read the Raid array. Let me know how it goes from there as I've been there and I know the feeling...